Absorbent pads fortified with thymol or carvacrol inhibit Escherichia coli   Farnham, S.1, van Veggel, N.1 and Bishop, C.2 1Centre for Equine and Animal Science, Writtle College, Chelmsford. 2Postharvest Technology Unit, Writtle College, Chelmsford.

Introduction Food waste The Institution of Mechanical Engineers reported (2012) 1.2-2 billion tonnes of all food produced is wasted annually Eliminating this waste can potentially provide 60-100% more food for consumption According to Waste and Recourses Action Program (2012), in the UK, by cost the largest groups of food wasted are: Fresh vegetables, salad and fruit (21%) Meat and fish (17%)

Detriments of microbial spoilage One of the major causes of food wastage in regards to fresh products is the limited shelf life A reason for limited shelf life is the deterioration of the food due to microbial spoilage E. coli O157:H7 causes numerous outbreaks of foodborne disease Bioactive food packaging: is the ability of such packaging to withhold desirable bioactive standards in optimum conditions for the preservation of food.

The promising prospects of carvacrol and thymol Essential oils, in particular those of the herbs thyme and oregano are shown to exhibit antimicrobial properties These properties are chiefly owing to the major components carvacrol and thymol Both compounds have the potential to extend shelf life of food products, thus reducing waste However, direct inclusion of carvacrol and thymol into food products negatively affects organoleptic properties This effect might be avoided by using the compounds in vapour phase as illustrated by Burt et al. (2007)

Aim The purpose of this study was to investigate the potential of absorbent pads releasing thymol and carvacrol vapours as bioactive food packaging strategies.

Figure 1: Disc volatilisation assay method. Methods A disc volatilisation assay was adapted from Burt et al. (2007) 100 μl of a 1 x 106cfu/ml E. coli culture was spread over a Mueller-Hinton agar plate Absorbent pads holding 100 μl of carvacrol or thymol solution (two concentrations of 50 or 100 mg/ml) were placed on the inside of the lid The base was immediately inverted and the plate was sealed with ParafilmTM Figure 1: Disc volatilisation assay method.

Assay 1: Cold storage duration Plates with a 42.5 mm diameter disc were stored at 4 °C for 0, 24, 48, 72 or 96 h followed by incubation at 37 °C for 24 h. Assay 2: Absorbent pad size Plates with discs (22.5, 32.5, 42.5, 52.5 and 62.5 mm diameter) received a dose of 100 mg/ml solution and were immediately incubated at 37 °C for 24 h.

Results (assay 1) The pads were equally effective for carvacrol and thymol in both 50 mg/ml and 100 mg/ml (P<0.05) Storage duration at 4 °C significantly increases inhibition of E. coli for both thymol and carvacrol in 50 mg/ml and 100 mg/ml doses (P<0.05)

Figure 2: Inhibition of E Figure 2: Inhibition of E.coli by 50 mg/ml (A) or 100 mg/ml (B) thymol and carvacrol over time.

Results (assay 2) Absorbent pad size significantly effects inhibition zone diameter for carvacrol and thymol (P<0.05) Table 1: Inhibition of E. coli by thymol and carvacrol using different absorbent pad sizes.

Conclusions Absorbent pads releasing carvacrol and thymol vapours can be used as an effective antimicrobial strategy to control E. coli in in vitro systems At 4 °C carvacrol and thymol stays volatile, resulting in a positive relationship between storage time and inhibition zone diameter of E. coli The significant association between absorbent pad size and inhibition of E. coli results in different optimal pad sizes for carvacrol and thymol

Future research To investigate the relationship between pad size, concentration of carvacrol and thymol, and inhibition of E. coli To investigate the inhibitory effects of carvacrol and thymol against E. coli on food products Apply this technique to industry-relevant packaging

Take home message Absorbent pads releasing carvacrol and thymol vapours are effective at inhibiting E. coli growth and may be a useful and sustainable control strategy in bioactive food packaging.

References & acknowledgement Burt et al. (2007) Int. J. Food Microbial., 119, 346-350. IMechE (2012) Global Food Waste Not Want Not. Available from http://www.imeche.org/docs/default-source/reports Global_Food_Report.pdf?sfvrsn=0 WRAP (2012) Final Report: Household Food and Drink Waste in the United Kingdom. Available from http://www.wrap.org.uk/sites/files/wrap/hhfdw-2012-main.pdf Absorbent pad material was kindly donated by